Why Osborne's 'granny tax' makes sense

Today's newspapers are full of predictable criticism for George Osborne's only budget surprise - removing the higher tax allowances enjoyed by people aged 65 and over. The Chancellor has bungled this announcement, slipping it into the budget statement as a 'simplification' when it is clearly a tax rise of around £200 a year for millions of pensioners. But is it really such as a bad idea?